ASME Y14.5 Envelope vs ISO Independency
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- Опубліковано 13 вер 2024
- This shows the major difference between the defaults in ASME Y14.5 and ISO-GPS standards related to tolerancing. Rule#1 and Independency are opposite defaults that a new user must know.
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I'm measuring opposed points of journals at the high limit or oversize per ISO 1101, but reporting under the low limit with the E modifier. What does this mean?
There is only one big question: Whats the feature function? An envelope is the suitable specification of a linear size, which is a member of a clearance fit function where both features have all six degrees of freedom in the clearance fit against together. If a high number of linear sizes in a specification are involved in that function, the dependency principle of ASME or a default envelope of ISO would be suitable. Take care: If there is no fit function of linear size or less than six DOF are left, this wouldn‘t be a perfect specification: A datumsystem is required with a maximum condition at the tolerancezone. With the greate ISO 2692 all defaults are set for a clearance fit: N, X, GN, GX and CZ. Additional ISO offers with the reciprocity condition the oppurtunity to match clearance fit with every tolance at linear size.
The ISO default for a linear size isn‘t the local size. It‘s the local point „LP“. All local points are perpendicular against an axis of the Gausscylinder.
Good comments. I agree, function should drive the specification. Envelope requirement is great for free fit holes and shafts. I do find envelope principle to be overly restrictive on bolt holes constrained to a datum system. Perfect form at MMC is not needed and rather the hole must only clear the virtual condition. Yes, reciprocity is a great ISO way to turn any gtol at MMC to a zero at MMC.
Good catch on linear size default for ISO. The local points perpendicular to the hole axis is slightly different than just ASME local size.
Hi! Thanks for the video! Will 2 different features, let's say ID and OD of the pipe, share the same axis by default in ASME? Or, do we need to add position tolerances between OD and ID in order to control wall thickness? Thank you in advance!
Two manufactured features can never be perfectly coaxial. So you specify a tolerance for how coaxial they must be (position tol). Another option is to define the size tol of one dia (either ID or OD) then specify wall thickness. The coaxiality (and size tol) is then indirectly controlled with the wall thickness tolerance.